/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * This file is part of retabel.
 *
 * Copyright (c) 2011 by individual contributors as indicated by the
 * @author tags. See the copyright.txt file in the distribution
 * for a full listing of individual contributors.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */

package org.retabel.persistence.dao;

import javax.ejb.TransactionAttribute;
import javax.ejb.TransactionAttributeType;
import javax.persistence.EntityManager;
import javax.persistence.NoResultException;
import javax.persistence.Query;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Root;
import java.util.List;

/**
 * Abstract super class for all dao classes with common used methods.
 * <p/>
 * <h3>Extra-Info</h3>
 * Created: 15:21 26.08.11
 *
 * @author Burt Parkers
 * @version 1.0
 */
@TransactionAttribute(TransactionAttributeType.SUPPORTS)
public abstract class AbstractEntityDaoBean<T> implements AbstractEntityDao<T> {

    /** The specific entity class, specified by the concretes class constructor. */
    private Class<T> entityClass;

    /** Default constructor. */
    public AbstractEntityDaoBean() {
        throw new RuntimeException("The calling class must define a specific entity class!");
    }

    /**
     * Constructor.
     *
     * @param entityClass the specific entity class.
     */
    public AbstractEntityDaoBean(Class<T> entityClass) {
        this.entityClass = entityClass;
    }

    /**
     * Returns the entity manager.
     *
     * @return the entity manager.
     */
    protected abstract EntityManager getEntityManager();

    @Override
    @TransactionAttribute(TransactionAttributeType.REQUIRED)
    public void create(T entity) {
        getEntityManager().persist(entity);
    }

    @Override
    @TransactionAttribute(TransactionAttributeType.REQUIRED)
    public T merge(T entity) {
        return getEntityManager().merge(entity);
    }

    @Override
    @TransactionAttribute(TransactionAttributeType.REQUIRED)
    public void remove(T entity) {
        getEntityManager().remove(getEntityManager().merge(entity));
    }

    @Override
    public T find(Object id) {
        try {
            return getEntityManager().find(entityClass, id);
        } catch (NoResultException e) {
            return null;
        }
    }

    @Override
    @SuppressWarnings("unchecked")
    public List<T> findAll() {
        CriteriaQuery criteriaQuery = getEntityManager().getCriteriaBuilder().createQuery();
        criteriaQuery.select(criteriaQuery.from(entityClass));
        return getEntityManager().createQuery(criteriaQuery).getResultList();
    }

    @Override
    @SuppressWarnings("unchecked")
    public List<T> findRange(int from, int maxResults) {
        CriteriaQuery criteriaQuery = getEntityManager().getCriteriaBuilder().createQuery();
        criteriaQuery.select(criteriaQuery.from(entityClass));
        Query query = getEntityManager().createQuery(criteriaQuery);
        query.setMaxResults(maxResults);
        query.setFirstResult(from);
        return query.getResultList();
    }

    @Override
    public int count() {
        CriteriaQuery<Object> criteriaQuery = getEntityManager().getCriteriaBuilder().createQuery();
        Root<T> rt = criteriaQuery.from(entityClass);
        criteriaQuery.select(getEntityManager().getCriteriaBuilder().count(rt));
        Query query = getEntityManager().createQuery(criteriaQuery);
        return ((Long) query.getSingleResult()).intValue();
    }

}
